Superconducting synchronous machines, i.e. synchronous machines having at least one superconducting winding, are already basically known in the prior art. In such cases the superconducting winding can be a rotor winding which must be cooled by a cooling device in order to maintain the operating temperature. For example it is known that the rotor can be provided with a hollow inner space in which a cooling medium introduced into this inner space evaporates on a heat-conducting winding carrier in order to cool the windings. The inner space thus acts as an evaporator space.
In order to insulate the cooled areas of the rotor, the “cold part” is usually surrounded by an insulating vacuum, meaning that a vacuum chamber rotating with the rotor is provided as part of the rotor. In such cases it has been proposed that the later vacuum chamber be pumped out and sealed off during the installation of the rotor in order to generate a static vacuum.
In practice however an absolute static vacuum is very difficult to achieve. As a result of leakage rates in the area of the flanged connections, welded joints and partly in the components used themselves it must be assumed that gases from the outer space will be able to intrude into the vacuum chamber to a greater or lesser extent during the operating life of the synchronous machine.
A number of approaches for improvement are known here in the prior art. On the one hand it has been proposed that by using so-called cryopumps, gases entering the chamber are frozen out and the vacuum thus maintained. With sufficiently small leakages this method is very successful and guarantees the operation of the machine even over longer periods. If however the cryopumps are heated together with the synchronous machine, the frozen-out gas also evaporates again and destroys the insulating vacuum. Further cooling down is then only possible with re-evacuation of the built-in rotor. For gases which cannot be frozen out at the operating temperature of the cold part of the rotor, for example hydrogen, helium or neon, other methods must be pursued. For hydrogen the use of so-called getter materials has been proposed, which bind the gases by adsorption, absorption or chemically.
It has further been proposed that the use of a static vacuum be dispensed with and that there be permanent pumping at the rotating vacuum chamber in that a pump flanged onto the rotor rotates along with the rotor. However, at high speeds in particular, this solution is ultimately not able to be implemented, since the centrifugal forces acting on the pump become too great with existing pump designs.